COS 151-2 - Historical vegetation maps reveal the magnitude of climate- and disturbance-mediated shift in forest type in Alberta, Canada

Background/Question/Methods

The rapidly warming climate of northern latitudes has a myriad of effects on boreal ecosystems, including the potential to alter wildfire regimes that drive landscape forest dynamics. It is difficult to disentangle the specific causes of forest cover changes, due to the inter-related effects of climate, wildfire, and human land use. Recent studies report an important increase in fire activity, fire severity (i.e., ecological impacts of fire), and the frequency of wildfires burning in short success (< 20 years), a phenomenon associated with tree regeneration failure and a change in forest cover type. In this study, we use historical vegetation maps from 1957, 1983 and 2022 to analyse 64 years of forest cover change across Alberta, Canada, in the context of increasing wildfire-mediated vegetation change.

Results/Conclusions

There has been a historical, wildfire-mediated shift from pure conifer forests to mixedwood and deciduous-dominated stands; 15.7% of burned areas (1957-1992) failed to recover to their original forest type within 30 years post-fire, instead recovering as pure aspen, with an additional 6.1% expansion of mixedwood forest. These forest type transitions towards an aspen-dominated system are magnified within the boundaries of short-interval reburns and along the southern boreal transition zone, leading to a transient but decades-long deforestation. Historical vegetation maps present an opportunity to assess the retrospective consequences of climate change, while also taking into account the effects of anthropogenic forest change driven primarily by, in our case, industrial resource extraction. This retrospective analysis reveals that substantial fire-driven vegetation conversion is well underway in central Canada, and that this conversion from conifer to mixedwood and deciduous forests is likely to become more pronounced as climate change continues to accelerate. Our findings are coherent with previously identified wildfire-induced vegetation change, but also reveal a wide variability in vegetation change trajectories across a heterogeneous, disturbance-driven forest.